Field of the Invention
This invention relates to a capacitive touch sensor, and in particular, it relates to a capacitive touch sensor integrated with an LCD or other types of display.
Description of the Related Art
Traditional capacitive touch sensors usually have two layers of transparent conductive traces. The traces are typically arranged perpendicular to each other. This type of capacitive sensors typically requires two patterned ITO layers, along with other conductive traces to route the signals. These ITO layers can be implemented either on two side of a single substrate or on one side of two different substrates, where the two substrates are bonded together. In a typical implementation, one layer of the traces is used to emit excitation signals, and other layer of traces is used to detect these signals to sense the presence of a finger or other object. An example of a double-sided touch sensitive panel is described in U.S. Pat. No. 7,920,129.
Almost all capacitive touch sensors are used together with LCD display panels, and are located above the LCD display panel. Touch screen integrated with LCD display have also been described. For example, U.S. Pat. No. 7,995,041 describes an “displays with touch sensing circuitry integrated into the display pixel stackup . . . Circuit elements, such as touch signal lines, such as drive lines and sense lines, grounding regions, in the display pixel stackups can be grouped together to form touch sensing circuitry that senses a touch on or near the display. An integrated touch screen can include multi-function circuit elements that can operate as circuitry of the display system to generate an image on the display, and can also form part of a touch sensing system that senses one or more touches on or near the display. The multi-function circuit elements can be, for example, capacitors in display pixels that can be configured to operate as storage capacitors/electrodes, common electrodes, conductive wires/pathways, etc., of the display circuitry in the display system, and that may also be configured to operate as circuit elements of the touch sensing circuitry.” (Abstract.) FIG. 7 of this patent shows a cross-sectional view of the display pixels.
U.S. Pat. No. 8,040,326 describes an integrated in-plane switching display and touch sensor. “This relates to adding multi-touch functionality to a display without the need of a separate multi-touch panel or layer overlaying the display. Instead, embodiments of the invention can advantageously utilize existing display circuitry to provide multi-touch functionality while adding relatively little circuitry that is specific to the multi-touch functionality. Thus, by sharing circuitry for the display and the multi-touch functionalities, embodiments of the invention can be implemented at a lower cost than the alternative of superimposing additional multi-touch related layers onto an existing display panel. Furthermore, since the display and multi-touch functionality can be implemented on the same circuit, they can be synchronized so that noise resulting from the display functionality does not detrimentally affect the multi-touch functionality and vice versa.”